The present invention relates to a method for making race rings for rolling bearings, specifically angular contact ball bearings. More particularly, the invention relates to a race ring for a bearing of this type which is at least partially plastic coated and produced from a metallic base component comprising an integral connected pair of complementary bearing races; that is, inner and outer rings, which may be formed in one piece and then easily separated or severed to provide the complementary inner and outer race rings for a bearing assembly.
There is shown in German Preliminary Application No. 2,153,597 a method for making rolling bearing races without a plastic coating. The blanks for the rings according to this process have an essentially S or U shaped profile configuration which are shaped in that configuration without cutting. The application does not set forth any provisions for easy separation of the race blanks or their further processing.
Another method for making bearing race rings for angular ball bearings is disclosed in German Preliminary Application No. 1,949,243. In accordance with the teaching of this patent, blanks are machined and then divided at a predetermined location in such a way that either two outer races or two inner races for a ball bearing are produced. It would not be possible to simultaneously produce in pairs consisting of an outer race ring and an inner race ring; and accordingly, in assembling the components of the bearing, the inner and outer race rings must still be selectively adjusted to each other based on dimensional tolerances.
With the foregoing in mind, it is an object of the present invention to provide a method of making plastic coated bearing race rings in complementary pairs wherein the same hardness properties and dimensional relationships are produced for an integral unit which comprises the inner and outer races of a bearing assembly. In this manner the assembly process can be simplified thus reducing expenses, and a high quality bearing is produced.
The method of the present invention consists essentially of the following steps:
a. forming the metallic base component to a generally S-shaped cross section with at least one annular separation juncture or bridge of reduced cross section at a location where after separation of the metallic base component, the separated elements form a complementary pair of bearing races;
b. hardening the metallic base component;
c. machining the raceway surfaces of the inner and outer ring sections of the base component simultaneously or successively;
d. plastic coating by an extrusion process; for example, the metallic base component to form plastic housing sections or enclosures near the bearing and side surfaces of the bearing race rings up to the running raceway surfaces section adjacent the separation juncture or bridge;
e. separating the metallic base component at the juncture or bridge to form the paired bearing rings.
The present process results in production, for example, of inner and outer race rings for an angular contact ball bearing which are integrally produced together up to the final assembly of the rolling elements, such as balls. Formation of the separation seam or juncture facilitates later separation of the rings in an easy and quick manner even in hardened constructions. The narrow connecting land or bridge is formed so that it is adequate or sufficient to withstand the stresses of subsequent processing and can be incorporated from one or both sides of the base component during the initial shaping or forming step without cutting or machining, thereby eliminating additional processing steps and attendant expense needed for this purpose. Furthermore, by forming the metallic base component to form complementary pairs of inner and outer races, during subsequent hardening of the metallic base component, each component has the same characteristics as a result of the simultaneous common processing. This is especially important when case hardening takes place and the inner as well as the outer race ring have the same core hardness, surface hardness, and case hardening thickness. Additionally, the narrow connecting land or bridge has a relatively great hardness in case hardened constructions so that separation at the bridge to form the separated inner and outer ring for a given pair can be accomplished very easily.
Furthermore, by grinding the raceway or running surfaces contacted by the balls of the inner and outer race rings simultaneously, the need for double handling of individual rings is eliminated; for example, clamping twice in a workpiece spindle so that an accurate rotation of both running surfaces is obtained. Additionally, the processing in this way insures a high degree of precision of the raceway or running surfaces dimensionally in relation to one another.
Subsequent to forming the metallic base component in the manner described above and while still in an integral or connected state, the inner and outer rings are placed together in an extrusion mold to form the plastic housing sections near their bearing and side surfaces. The plastic layer or housing for each of the race ring components is split or interrupted adjacent the connecting land or bridge near the running or raceway surfaces. Formation of the plastic housing in this manner also results in a high degree of dimensional precision so that the complementary rings produced are advantageously adjusted to each other with respect to rotation and bearing dimensions.
At this phase of the process, the inner and outer rings of each component may be separated very readily at the hard and thin connecting land or bridge. For example, the inner connected ring components may be simply separated by slight elastic oval deformation of one of the rings or a radial or axial snapping sufficient to break the connecting bridges or lands. The bearing races can then be used without further processing for the assembling of the rolling elements. For maximum precision advantages, the two bearing rings separated from one another are used for one and the same bearing assembly since they complement one another.
In accordance with another feature of the present invention, the separation of the base component assembly at the connecting bridge may be accomplished by snapping the inner race ring in an axial direction by means of the inner ring of another pair of bearing races after insertion of a row of rolling elements such as balls. Consequently, two process steps are combined into one; and the production cost for the assembled bearing can be further reduced. Moreover, it is possible to stack a large number of connected inner and outer ring assemblies and to insert each time a row of balls between the stacked assemblies. Simultaneous separation and final assembly of the pairs is then achieved simply by applying a force, for example, to the inner race ring portion of the assembly at the top of the stack while the outer race ring portion of each assembly is supported at the bottom of the stack. As a result, in a single operation, all inner race rings of the stack are simultaneously separated from the outer races with the balls of each assembly positioned in place between the race rings. If done in this manner, the inner race ring at the bottom of the stack is left over and can be used as the top inner race ring for the next stack, for example.
In accordance with another feature of the bearing assembly made in accordance with the present invention, the housing section for one of the race rings is provided at one axial end with an annular radially directed elastic retaining rim which projects beyond the raceway surface and serves to retain the elements of the bearing assembly as an integral unit and prevent accidental separation thereof after assembly. The retaining rim is constructed in such a way that it does not interfere with the assembly of the components of the bearing since it is elastic and is constructed in its radial dimensions in such a way that it is radially deformed by the axially sliding rows of balls to produce a snap effect when assembling the elements of the bearing assembly. It is noted that shape, dimensions, and elasticity of the retaining rim may be selectively varied depending on the type of bearing assembly. The rim may be provided with an inclined frusto conical surface to provide an easier elastic deformation of the retaining ring by the rolling elements during the assembly process.
Still another feature of the race ring assemblies of the present invention is the provision of radially directed projections circumferentially spaced over the peripheral edge of the metallic base component of the races which serve to anchor the race rings in the plastic housing to prevent relative rotation of the two during operation of the bearing. The projections may also extend through and beyond the plastic bearing housing sections to engage the surfaces of a bore or shaft within which the bearing assembly is mounted to provide in some applications an accurate fit upon installation in a housing bore or on the shaft. Further, even though the present invention has been illustrated and described herein in connection with assemblies comprising a single inner race ring and a single outer race ring, it is, of course, to be understood that two outer races or two inner races in pairs can also be produced according to the method of the present invention and incorporate all of the advantages described above. This method would be particularly suitable for rolling bearing assemblies incorporating two rows of rolling elements, for example, in a double row angular contact ball bearing.